Viscosity Turbulence Models Research Articles

Development and validation of a lifting‐line code associated with the vortex particle method software Dorothy

AbstractThis paper presents a lifting‐line implementation in the framework of a Lagrangian vortex particle method (LL‐VP). The novelty of the present implementation lies in the fluid particles properties definition and in the particles shedding process. In spite of mimicking a panel method, the LL‐VP needs some peculiar treatments described in the paper. The present implementation converges rapidly and efficiently during the shedding sub‐iteration process. This LL‐VP method shows good accuracy, even with moderate numbers of sections. Compared to its panel or vortex filaments counterparts, more frequently encountered in the literature, the present implementation inherently accounts for the diffusion term of the Navier‐Stokes equations, possibly with a turbulent viscosity model. Additionally, the present implementation can also account for more complex onset flows: upstream ambient turbulence and upstream turbine wakes. After validation on an analytical elliptic wing configuration, the model is tested on the Mexnext‐III wind turbine application, for three reduced velocities. Accurate results are obtained both on the analytical elliptic wing and on the New MEXICO rotor cases in comparison with other similar numerical models. A focus is made on the Mexnext‐III wake analysis. The numerical wake obtained with the present LL‐VP is close to other numerical and experimental results. Finally, a last configuration with three tidal turbines in interaction is considered based on an experimental campaign carried out at the IFREMER wave and current flume tank. Enhanced turbine‐wake interactions are highlighted, with favourable comparisons with the experiment. Hence, such turbine interactions in a farm are accessible with this LL‐VP implementation, be it wind or tidal energy field.

Sensitive analyses of flow property to turbulence model in swirls simulation within aquaculture tanks

Water swirls in tanks with bottom drain(s), which is observed in aquaculture tanks. Numerical simulation of the swirling field with the general two-equation turbulence models fails to describe the swirling phenomenon and the investigating results are less convincing. This study simulates the swirling flow fields with four categories of turbulence models, they are the laminar model, the turbulent-viscosity model, the Reynolds stress model, and the Large Eddy Simulation model. Results show that the swirling phenomenon is successfully numerically reproduced except for the turbulent-viscosity model. Although the flow properties predicted with the turbulent-viscosity model are different from other turbulence models, the results are meaningful from the perspective of statistical items (mean, standard variation, uniformity, PDF, CFD). For cases with swirls, the flow field can be divided into a forced vortex and a free vortex, and their tangential velocity profiles can be described with a theoretical formula. Considering the numerical cost and the reproduction of experiments, the Reynolds stress turbulence model is preferable in studies of the flow properties of aquaculture tanks.

Тестова задача моделювання течії у ступені компресора Rotor 37

The subject of the study is the dependence of the degree of pressure increase on the airflow in the impeller of the axial compressor degree. The object of study is the Rotor 37 axial compressor. The purpose of this study was to select a turbulent viscosity model when conducting a test task in the Rotor 37 compressor. To achieve this goal, the following tasks were solved: to create a three-dimensional model of the object under study; develop a grid model of the object under study; to simulate the flow in a certain range of air flow; to compare the data of numerical and physical experience; evaluate the flow visualization in the Rotor 37 axial compressor stage for all studied turbulent viscosity models. When studying the flow in the stage of the axial compressor Rotor 37, the numerical experiment method was used. The flow simulation was carried out by solving the system of Navier-Stokes equations, which was closed by the turbulent viscosity model. The study used seven turbulent viscosity models: k-ε, k-ε EARSM, SST, BSL, BSL Reynolds Stress, SSG Reynolds Stress, and QI Reynolds Stress. For simulation, a computational grid was built with the adaptation of the boundary layer. This study presents the results of a flow simulation test problem in the Rotor 37 compressor. The results of the study show that all the tested turbulent viscosity models can be used to simulate the flow in an axial compressor. However, the flow calculation with the SSG Reynolds Stress turbulent viscosity model has the smallest error. An analysis of the visualization of streamlines in the interblade channel of the Rotor 37 compressor showed that in all cases, the flow pattern with all turbulent viscosity models is similar. Some differences are observed when modeling the flow with the BSL Reynolds Stress and SST turbulence models. An important factor that should also be taken into account when modeling is the calculation time. In this case, the shortest calculation time was observed for simulation with SST model. Scientific novelty and practical significance is that new data were obtained when testing the following turbulent viscosity models: k-ε, k-ε EARSM, SST, BSL, BSL Reynolds Stress, SSG Reynolds Stress, QI Reynolds Stress. The results obtained made it possible to choose a turbulent viscosity model for further research.

Оцінка впливу канавок у дифузорі на втрати повного тиску

The subject of the study is the total pressure in the diffuser channel with passive control of the boundary layer. The object of this research is a diffuser channel with riblets. The mechanism of total pressure reduction due to the presence of longitudinal grooves on the streamlined surface is related to the strengthening of viscous forces acting in the transverse direction caused by them. These forces generate a relatively calm flow inside the riblets, which pushes out the turbulent flow, which causes surface friction, pushing it away from the surface. Thus, the process of generation and growth of elongated wall turbulent formations. In addition, in the presence of riblets, a change in the pressure field in the transverse direction is possible, as well as the creation of a quasi-two-dimensional flow in the immediate vicinity of the wall. In this work, the aim of research to investigate the influence of riblets on total pressure loss in the diffuser channel with the purpose of evaluating the influence of riblets on the change in the nature of the flow and the change in pressure, using numerical modeling. To study the nature of the flow in the diffuser channel, we resolved the following tasks: a diffuser channel was modeled with the following dimensions: length L=50 mm, hydraulic diameter at the inlet X=25 mm, hydraulic diameter at the outlet Y=40 mm, riblets diameter d=4 mm, number of riblets n =4 and n=8. The study was compared with a diffuser with the following dimensions: length L=50 mm, diameter at the inlet X=25 mm, diameter at the outlet Y=40 mm. To research the flow in the diffuser, the method of numerical experiment was chosen. An unstructured calculation grid was used in the diffuser for the research. The calculation of the turbulent gas flow was performed by numerically solving the averaged Navier-Stokes equations. During the numerical simulation of the flow, the Reynolds stress turbulent viscosity model will be used. As a result, using a diffuser with riblets increases the coefficient of hydraulic resistance compared to a smooth diffuser. The resistance reduction mechanism does not work due to the relatively short length of the diffuser and small longitudinal vortices of the riblets scale do not have time to form. There are pressure increasing instead of laminization of the flow and pressure decreasing. Scientific novelty - received new data on the effect of riblets in the diffuser channel on the total pressure loss coefficient. Practical significance - the obtained results can be used to control the boundary layer in diffuser channels (in diffuser compressor grates) to improve their characteristics.

Аналіз впливу мотогондоли на силу тяги вентиляторного контуру турбовентиляторної приставки

The subject of this study is the interaction between the engine nacelle of a three-circuit turbojet engine and a turbofan attachment. The object of this research is a model of a cylindrical engine nacelle and a fan part of the impeller of a turbofan attachment. The aim of this study was to evaluate the influence of the engine nacelle on the thrust force of the fan circuit of a three-circuit turbojet engine, taking into account the influence of the operation of the turbofan attachment. Tasks: to simulate the flow around the engine nacelle with a turbofan attachment and without a turbofan attachment; calculate the thrust force of the turbofan attachment. The studies were carried out using the method of numerical experiment. The system of Navier-Stokes equations was closed by the turbulent viscosity model SST Gamma Theta Transitional No. 4. The results of the study showed that the reactive thrust of the fan circuit of the turbofan attachment increases by 0.87-6.15% when operating at an altitude of 0 km, 9 km, 11 km and the range of Mach numbers at the input from 0.2 to 0.5. When flowing around the engine nacelle without taking into account the influence of the turbofan attachment, it is characteristic that the velocity field at the inlet is uniform, except for the zone with a boundary layer near the surface of the engine nacelle. However, during operation of the turbofan attachment, the flow pattern changes radically and the thickness of the boundary layer decreases, and the flow in front of the fan is uneven. A characteristic feature of the turbofan attachment, which is associated with the heating of the intermediate housing between the turbine and fan housings, has a positive effect on reducing the thickness of the boundary layer, wall heating contributes to an increase in the stagnant flow velocity due to viscous forces. The presence of a boundary layer on the engine nacelle does not adversely affect the flow in the fan circuit of the turbofan attachment, and the fan of the turbofan attachment does not adversely affect the engine gas generator. The scientific novelty and practical significance of this work lies in obtaining new data on the effect of the engine nacelle on the thrust force of the fan circuit of a three-circuit turbojet engine, taking into account the influence of the operation of the turbofan attachment. The results obtained can be used to optimize the turbofan attachment of a three-circuit turbojet engine.

Конвективный теплообмен и трение в тонком ламинарно-турбулентном пограничном слое на проницаемой поверхности затупленного конуса малого удлинения

Solving the problem of calculating convective heat transfer and friction in the laminar-turbulent boundary layer involves the need for numerical integration of differential equations, supplemented by those or other semiempirical models of apparent turbulent viscosity, which should be validated on the results of experimental studies, carried out in conditions, providing simulation of the gas dynamic picture of body flowing by a gas stream. Unfortunately, at present, there are no literature data on studies of laminar-turbulent heat exchange on the permeable surface of a blunted body, and under these conditions, one has to go by the way of comparing the calculated data with the results of experiments carried out on sharp bodies. Literature sources describe the results of studies carried out for a hemisphere, in which one of the semi-empirical models of apparent turbulent viscosity is used, tested on the results of experiments carried out on the impermeable surface of such shaped body. In this case, it was possible to obtain a physically consistent picture of the influence exerted by blowing gas through the wall on the degree of blocking of the convective heat flow. In the absence of qualitative experimental data on this issue, it seems reasonable to apply in practice the considered semi-empirical model of apparent turbulent viscosity to estimate the degree of blocking of convective heat flow and friction under the specified conditions. This article is devoted to the solution of a similar problem for the lateral surface of a blunted cone

Single-Layer Algebraic Model of Apparent Turbulent Viscosity and Modified Effective Length Method

Single-Layer Algebraic Model of Apparent Turbulent Viscosity and Modified Effective Length Method

Two-equation turbulent viscosity model for simulation of transitional flows: An efficient artificial neural network strategy

Laminar-to-turbulent transition phenomena are ubiquitous in natural and industrial flows. As to the Reynolds-averaged Navier–Stokes (RANS) simulation method, the workhorse for accurate prediction of such flow regime boils down to the consideration of the transition effect in turbulence modeling. In this paper, an industrial–practical transition–turbulence model with excellent accuracy, robustness, and efficiency is established by the fully connected artificial neural network (ANN), which maps the relation between the RANS mean flow variables and an intermittency factor. A one-equation local correlation-based transition model coupled with Menter's shear stress transport (SST) model is taken as the benchmark. The present two-way coupling ANN model is trained with two National Advisory Committee for Aeronautics (NACA) airfoils, that is, NACA0012 and NACA2418, at various angles of attack and Mach numbers, while tested with the A-airfoil, NACA0015, and RAE 2822 supercritical airfoils in different flow states. The a posteriori test results manifest that the mean pressure coefficient, skin friction coefficient, size of laminar separation bubble, mean streamwise velocity, Reynolds shear stress, and lift/drag/moment coefficient predicted by the ANN model are all in good agreement with those given by the benchmark transition-based SST model. Furthermore, the ANN model exhibits higher calculation efficiency and convergence speed than the traditional transition-predictive SST model. The present work may pave a new way for machine learning methods to be used in integrated transition–turbulence modeling toward industrial applications.

Моделювання течії в надзвуковій компресорній решітці

The design of modern aircraft engines cannot be imagined without numerical simulation methods. The advantages of numerical simulation at the first stages of creating engines are obvious: the ability to explore different geometric models in a fairly short time, while the accuracy of calculations reaches 5 ... 15%. An integral part of the numerical experiment is conducting test problems, because of which it is necessary to identify the necessary topology of the computational grid and the turbulent viscosity model. The current study conducts a test problem of flow simulation in a supersonic compressor cascade-based on the STFF rotor to select the topology of the computational grid and the turbulent viscosity model for closing the system of Navier-Stokes equations. In this work, four variants of the computational grid and four models of turbulent viscosity were studied. The time step was automatically changed. The maximum time over time was 0.00005…0.001 s. Control points were set in front of the grating and behind it, where the value of the Mach number was displayed. When calculating, the value of the Mach number in front of the grating was selected by changing the value of the velocity at the input. The calculation was terminated when the values of the Mach numbers at the input and output of the cascade were reached, as well as constant values of the residuals, which did not change during subsequent iterations. 4 variants of the structured type computational grid were built. Grid No. 3 was chosen for further calculations since it provides sufficient similarity with the test results, and it also has a smaller size, which makes it possible to speed up the calculation. Next, calculations are performed for different types of turbulence models. The turbulence models SST, SST GTT, k-ω and RNG k-ε were considered. For all turbulence models, the boundary layer height was chosen based on the condition Y+ < 1. An analysis of the calculation results showed that the smallest error was obtained in calculations with the SST GTT turbulence model. This paper presents a comparison of the density distribution in the cross-section of the cascade with a schlieren photograph obtained from a field experiment. A qualitative analysis of the obtained results shows that the flow patterns around the STFF-based compressor grate are of a similar nature, in particular, in the interblade channel and edge wakes behind the cascade. Thus, for further research to study the flow in the fan, the topology of the Mesh3 computational grid and the turbulent viscosity model SST GTT were chosen.

Numerical Simulation of the Nonstationary Process of the Shot Based on the Navier – Stokes Equations

This paper gives a spatial mathematical formulation of the problem of internal ballistics based on the Navier – Stokes equations, taking into account the swirl of the flow due to the rotation of the projectile. The k-e model of turbulent viscosity is used. The control volume method is used for the numerical solution of systems of equations. The gas parameters at the boundaries of the control volumes are determined by the method of S. K. Godunov using a self-similar solution to the problem of the decay of an arbitrary discontinuity. The MUSCL scheme is used to increase the order of approximation of the difference method. For equations written in a cylindrical coordinate system, an orthogonal difference grid is constructed using the complex boundary element method. A comparative analysis of the results obtained with different approaches to modeling the process of an artillery shot is given. Quantitative data are presented on the influence of factors not previously taken into account on the characteristics of the process.

Shell model of turbulent viscosity for the boundary layer

The problem of numerical simulation of developed turbulent flows is usually reduced to the choice of one or another closure of the mean field equations. It is hardly possible to find a universal solution to this issue; nevertheless, the development of an approach based on general principles remains an active research topic. This paper proposes a model of turbulent viscosity described in terms of the characteristics of velocity field fluctuations calculated on the basis of shell models. These models reproduce correctly the scale distribution of the turbulent energy and the spectral energy fluxes for hydrodynamic flows of various physical nature. Shell models are constructed using symmetry properties and conservation laws of the complete system of equations, as well as an assumption on homogeneity and isotropy of turbulence. Phenomenological relations implying specific spectral laws are not involved. In the developed approach, we did an attempt to determine the turbulent viscosity, while maintaining the universality and flexibility of shell models. The resulting mathematical formulation is a set of models for large (mean field equation) and small (cascade model) scales, as well as closing relations. The model implements energy conjugation of variables of different scales, which provides a nonlinear relation of fields at different levels. Taking into account the influence of the mean field on the energy distribution of turbulent fluctuations is a distinctive feature of the proposed approach. Numerical solutions are obtained for the flow in a plane infinite channel at various Reynolds numbers. It is shown that the obtained results are consistent with modern concepts of the logarithmic profile of the velocity field in the boundary layer. The physical meaning of model parameters is substantiated. Asymptotic solutions that qualitatively correspond to the Prandtl model are found.

Конвективный теплообмен и трение в тонком ламинарно-турбулентном пограничном слое на непроницаемой боковой поверхности затупленных конусов малого удлинения

In order to provide a high-quality solution to the problem of computing convective heat transfer parameters in a laminar-to-turbulent boundary layer, it is necessary to numerically integrate differential equations describing that layer, completed by semi-empirical turbulent viscosity models, said models having been tested by comparing their output to the results of experimental investigations where the gas dynamics of a gas flow around a body is correctly simulated. Developing relatively simple yet adequately accurate computation methods becomes crucial for practical applications. To date, the effective length method, being simple yet apparently boasting an acceptable accuracy, has become the most widespread technique for solving this problem in aircraft design and aerospace technology. However, this statement is not correct for large Reynolds numbers on a hemisphere. Under these conditions, semi-empirical apparent turbulent viscosity models provide significantly better matches to experimental data. The paper analyses the feasibility of using a similar approach for the lateral surface of a blunted cone featuring a low aspect ratio. We describe a new efficient approach to solving this problem, demonstrating a high accuracy and maximum simplicity when used in practice. We check the results of systematic computations using our method against comparable data obtained via the most frequently cited approaches to solving this problem

Обґрунтування моделі турбулентної в’язкості для дослідження характеристик співвісного гвинтовентилятора і вхідного пристрою ГТД

The issues of substantiation of the most rational, based on adequacy, model of turbulent viscosity for mathematical modeling of the flow near the propfan and in the inlet of the turbine-propeller engine are considered. It was found that at present there is no universal turbulence model for determining the parameters of the boundary layer, energy loss in the flow, and laminar-turbulent transition. Analysis of the results of previous studies showed that there is a need to select and justify a turbulent viscosity model for each type of research object. The task of modeling the flow near the propfan and in the inlet device of the power plant was performed using the ANSYS CFX software product, which allows using various standard mathematical models and tools for modeling turbulent flow. The object of research is an annular axial inlet device, in front of which there is a coaxial propfan with two rows of propellers: the first row has eight blades, the second - six. 7 types of models of turbulent viscosity, which most fully describe the phenomena in the flow around the propfan and the inlet device, have been investigated: k-ωmodel; SSТ (shear stress transport) SST Transitional №1 Fully turbulence; SST Transitional №2 Specified Intermittency; SST Transitional №3 Gamma model; SST Transitional №4 Gamma theta model; SST Transitional №5 Intermittency. The results of mathematical modeling of the flow near the propfan and in the inlet device at the corresponding operating mode of the turbopropfan engine using the selected models of turbulent viscosity, the total pressure value in front of and behind the inlet device was obtained to determine the total pressure recovery coefficient in it and the value of the propfan thrust. The value of the recovery factor of the total pressure in the inlet device and the propfan thrust are compared with the flight test data of the prototype. An analysis of the comparison of the values of the total pressure recovery factor in the inlet device and the propfan thrust showed that the use of the SST Transitional №4 Gamma theta model allows obtaining the value of the total pressure recovery factor in the inlet device and the propfan thrust that is closest to the flight test results.

Моделювання течії в співвісному гвинтовентиляторі з управлінням примежовим шаром

The development and improvement of turboprop engines are one of the important tasks of modern aircraft engine building. Propeller performance significantly affects the overall efficiency of turboprop engines. An important issue is to increase the trust of the propeller or propfan. In this matter, promising energy methods for increasing lift deserve special attention. Energy methods for increasing the lift force are based on the use of additional energy from the power plant to improve the flow around the blade and increase its bearing properties. The purpose of this work is to assess the influence of the boundary layer control on the blades of a coaxial propfan on the thrust. A coaxial propfan was chosen as the object of research. The rotor fan consists of two rows of blades, the first row has eight blades, the second - six. The peripheral diameter of the blades of the propfan is the same and amounts to 4.5 m. The cruise mode of operation was selected for the study. Modeling the flow in a coaxial propfan was based on the solution of the Navier-Stokes system of equations, which was closed by the SST Gamma Theta Transition model of turbulent viscosity. The computational grid consisted of 20 million cells, type-block, structured and unstructured with an adaptation of the boundary layer. In this study, an active boundary layer control method was chosen. The boundary layer was controlled only on the blades of the first row of the propfan. In the peripheral region of the blade, an additional mass of air was blown out through the slot, at a distance of 70 % of the profile chord. Blowing out a thin jet near the blade wall to increase the flow energy serves as an effective means of controlling the flow separation and increasing the bearing capacity of the propfan blade. Analysis of the simulation of the flow in a propfan with control of the boundary layer showed that the addition of energy to the boundary layer contributes to the filling of the velocity profile in the boundary layer, leads to a decrease in resistance and an increase in the thrust of the propfan. The results of the study showed that for the studied scheme of blowing out an additional mass of air on the propeller blades, it is possible to increase the thrust force up to 100 N. In the future, it is planned to investigate other schemes for controlling the boundary layer to increase the thrust of the coaxial propfan.

RANS simulation of unsteady cavitation around a Clark-Y hydrofoil with the assistance of machine learning

In the present paper, a novel machine-learning-assisted RANS method is proposed and utilized to investigate the unsteady cavitating flow around a Clark-Y hydrofoil. A data-driven machine learning model for turbulent eddy viscosity (TEV) is constructed based on high-fidelity LES results first and then makes a prediction for TEV in RANS simulation. The machine-learning-predicted TEV successfully imitates the TEV distribution characteristics of LES that there is a concentration around cavities and negative TEV in the wake. Based on the more accurate TEV field, the machine-learning-assisted RANS method makes more accurate predictions about velocity profile and basic performance parameters of the hydrofoil and gives a better representation of shedding process of sheet cavitation when compared with original RANS results. Finally, generalization performance of the machine learning model is assessed by simulating cavitating flows under different inlet velocity conditions. The results indicate that cavitation exhibits more periodicity with the decrease of inlet velocity in the range of investigated conditions, which may be associated with different TEV distribution characteristics.

Computational Fluid Dynamics (CFD) Study on the Effect of the Number of Blades on the Performance of Double-Stage Savonius Rotor

Wind energy is known as renewable energy with the properties of the free, abundant and readily available source of energy. Wind power has now been seen as an alternative way to generate electricity. However, the existing wind turbines to harness this energy, which is used to transform wind kinetic energy into electricity still suffer low conversion capabilities. This study is therefore set out to evaluate the performance of a double-stage Savonius-type rotor while aiming to examine the effectiveness of this technique in increasing the efficiency while overcoming the inherent low inefficiency of the Savonius rotor. The simulations involved the use of the K-omega SST as the turbulent viscosity model. Three simulation models based on a different number of blades on the double-stage model are tested in terms of torque, power, torque coefficient and power coefficient. It is concluded that the double-stage technique was capable of enhancing the performance of the Savonius rotor. It was observed that more blades on a double-stage rotor have a negative effect on the performance of the Savonius rotor in terms of both torque efficiency and power efficiency. Comparing the three models, it was found that the two-blade model of the double-stage produced more torque and power output compared to the other three-blade and four-blade models of the double-stage Savonius rotor. Furthermore, the highest conversion efficiency in terms of power among all models occurs at the TSR of 0.6 with a corresponding maximum power coefficient of 18.4%.

Numerical convergence of volume of fluid based large eddy simulations of atomizing sprays

This paper presents three volume of fluid (VoF)-based methods for large eddy simulations of atomizing sprays with different treatments of the unresolved interface. The turbulent filtered VoF model uses conventional turbulent viscosity models to close the combined interfacial and turbulent sub-grid fluctuations. The hybrid turbulence filtering and artificial compression model includes an additional artificial compression term that is applied along regions where the liquid–air interface is continuous, while conventional turbulence filtering is activated in regions with discrete liquid objects. The new explicit volume diffusion model (EVD) is based on the concept of averaging the VoF equations over explicitly defined physical volumes that are independent of the numerical grid. Closure models of the sub-volume flux and stress terms introduce explicit volume diffusion and explicit volume viscosity that are physically defined and linked to the volume size. Numerical convergence is achieved by reducing the grid size while keeping the explicit volume size constant. The models are tested for two experimental atomizing spray cases with different Weber numbers. The superior numerical convergence of the EVD model is demonstrated by analysis of the mean and rms of the volume fraction and velocity fields. Two models for the surface tension force are investigated for the EVD simulations. Compared with the simple surface tension model which neglects sub-grid fluctuations, an improved volume-averaged model based on fractal properties of wrinkled sub-volume interfaces gives better predictions of the mean volume fraction relative to the experimental data but requires selection of a model constant.

New consideration of lateral boundary treatment for meso- and micro-scale nested PBL simulations over complex terrain

A detailed planetary boundary layer (PBL) flow over complex terrain can be simulated by nesting mesoscale numerical weather prediction (NWP) models and microscale computational fluid dynamics (CFD). When fully prescribed lateral boundaries are encountered, the over-specified treatment of CFD or limited-area models may result in ill-posedness and numerical instabilities. Such behaviors are due to inconsistent governing equations, turbulent viscosity models, and underlying surfaces between meso- and micro-scale formulations. In this study, by applying the relaxation treatment in marginal zones of CFD, its wind components are forced toward the externally specified NWP values. The relaxation schemes, deduced from simple advective transport equations, are optimized using genetic algorithms. Their numerical abilities in absorbing wave reflections on shallow-water systems are more efficient than the published approach. Then, key questions concerning the selection of relaxation strength, turbulence model constants, and prognostic variables specified on NWP–CFD nested boundaries are systemically investigated in the neutrally stratified Askervein Hill case. The relaxation scheme from simpler systems also performs effectively in CFD and decreases the adaption distance of wind velocities near over-specified outlet boundaries. A full set approach to obtain well-posed PBL solutions from the microscale domains sustained with inflow boundaries from NWP is proposed and validated.

Simulation of Biomass Combustion with Modified Flue Gas Tract

The combustion of biomass is accompanied by the formation of particulate matter, the presence of which in the atmosphere harms human health. It is important to show the issues of reducing these pollutants and their impact on human health. This article focuses on the process of biomass combustion. The used model consists of two parts: the combustion chamber and the flue gas tract. The article shows four types of modification of the flue gas tract designed to reduce the amount of particulate matter in the atmosphere. Baffles are located in the flue gas tract, which is designed to capture the particulate matter. The final model is simulated by turbulent–viscosity models, k-ε realizable model, and then k-ω shear stress transport model. The interaction between turbulence and chemical reactions is expressed by using the Eddy Dissipation Concept model. The results then show different profiles of temperature, velocity, and particle distribution. Based on the evaluated data from two different calculations, it can be concluded that the baffles have a significant effect on the reduction of particulate matter in the atmosphere. The used baffles are able to capture mainly particles with a diameter greater than 100 µm. A significant number of particles with a diameter lower than 100 µm flows from the flue gas tract to the surrounding environment.

Experimental and Numerical Investigation of the Mixing Ratio for Various Vane Swirlers of the Combustion Chamber of a Gas Turbine Engine

The paper investigates the swirling flow behind the GTE combustion chamber swirler with blades installed under different angles. The mixing ratio in the flow is experimentally analyzed and compared with the estimated values obtained by a numerical approach and using various models of turbulent viscosity.